INSULATION 71 Getting to grips with Part L


A year on from the latest, and highly significant, changes to Part L in England, Chris Pateman of Engineered Panels in Construction (EPIC), explores why the current requirements are so important, and what specifiers need to know going forward now that the transition period has ended


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fter sitting in the doldrums for almost a decade, Part L of the Building Regulations finally got an overhaul in June 2022 and set us back on the path towards a net zero carbon built environment – a target that new non- domestic buildings were originally planned to meet by 2019. With a 27% reduction in emissions over the 2013 standard being required at this stage, there is still a long way to go before hitting net zero, however there were some important changes introduced in the most recent update that will help to pave the way to that goal. This article explores the requirements that directly relate to the building envelope for non-domestic buildings, but full guidance on all aspects can be found in Approved Document L2 2021 (ADL2).


There was previously a loophole in the transitional arrangements which allowed developers to continue to build to the previous standards, provided work had started on one building before the end of the transition period. This meant phased projects and developments of multiple buildings could continue to be built to a lower standard. Under the new requirements, any buildings not started within the transition period are subject to the current regulations. The transition period to ADL 2021 finished in June 2023, so all new construction must now meet this version.


Improvements in insulation – what changed?


Previously the building fabric limiting values were not particularly demanding, and in most cases, buildings needed to meet the much more rigorous values set out in the notional building models to achieve compliance. The 2021 minimum U-value requirements now more closely reflect


ADF JULY/AUGUST 2023


those of the notional building, and the maximum allowable ‘backstop’ level of air permeability has also been tightened.


Building Fabric Limiting Values (England)


ADL2A 2013 (with 2016 amendments)


Flat Roof


Pitched Roof Walls Floors


Rooflights* Air permeability


ADL2 2021


0.25 W/m²K 0.18 W/m²K 0.25 W/m²K 0.16 W/m²K 0.35 W/m²K 0.26 W/m²K 0.25 W/m²K 0.18 W/m²K 2.2 W/m²K 2.2 W/m²K 10 m3/(hr∙m2) 8 m3/(hr∙m2)


(Note that rooflights were previously measured in the vertical plane and are now measured in the horizontal plane)


The same limiting values apply for new and replacement elements in existing buildings in England.


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Factory engineered jointing helps to ensure high levels of airtightness, often achieving 2 m3/(hr∙m2) at 50 Pa or better


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